1. Field of the Invention
The present invention relates to an electrically powered mechanism for expanding and contracting antenna. More specifically, the invention relates to a mechanism for operating an expansion/contraction operation member which efficiently drives a strip such as a wire, which multiplies the drive force, is simple in construction, does not permit the wire to be buckled, and enables the wire to be easily replaced.
2. Prior Art
A variety of systems have heretofore been placed in practical use to pull out or insert a wire connected to an antenna that is mounted on a vehicle such as a motor car and that is expanded or contracted by a rotary member driven by a motor. Such mechanisms for expanding and contracting the antennas can be roughly classified into:
(1) Those of the generally so-called drum type in which a base end of the wire is fastened or is loosely fastened to a drum for winding the wire, and the wire is sent or is taken up by rotating the drum, such that the antenna is expanded or contacted by the wire as disclosed in Japanese Utility Model Publication No. 10431/1969;
(2) Those of the so-called roller type in which a U-shaped or a V-shaped groove is formed along the circumference of a rotary member, a pressing roller is provided to fit a wire to the groove and to bring the wire into intimate contact with the back portion to produce the pressing action relying upon the frictional force, and the pressing force or the drawing force is obtained by the rotation of the roller, or a corrugation is formed on both sides of the groove of the rotary member and a flexible wire is brought into engagement with the rotary member, as disclosed in Japanese Utility Model Publication No. 27972/1964;
(3) Those of the so-called pinion-rack system in which engaging teeth are formed along the periphery of the rotary member, the wire is imparted with a tooth form that meshes with the engaging teeth, and the wire is driven based on the relationship of rack and pinion, as disclosed in, for example, Japanese Utility Model Publication No. 18323/1983; and
(4) Those of the so-called tenor system in which the rotary member described in (2) above has an annular groove 31 formed in one surface thereof as shown in FIGS. 7 and 8, pawls 32 are formed maintaining a distance along the circumference of the annular groove 31 to prevent slipping relative to a wire 33 that has a round shape in cross section, and the expansion or contraction operation is carried out relative to the case body by the turn of the rotary member 30, as disclosed in, for example, U.S. Pat. No. 2,896,870.
The above-mentioned conventional devices, however, have disadvantages and defects, and are not necessarily desirable.
That is, in the device of the drum type mentioned in (1) above, buckling phenomenon takes place due to the size of the internal volume of the drum which provides the requisite capacity for accommodating the wire in the drum. That is, when the antenna is stretched and only a small amount of the wire left in the drum thereby creating a sizeable empty space, the wire buckles in the space. When an expanding force of greater than, for example, 5 kg is required, it becomes difficult therefore to obtain the expanding action effectively. In the drum-type device, furthermore, the wire must be properly attached to the drum to carry out expansion operation and contraction operation stably. When it is required to repair or renew the wire, the operation mechanism must be removed from the vehicle and must then be disassembled, thereby creating difficulties from the standpoint of after-sale service. Further, a large drive torque is required to drive the drum.
In the device of the roller type mentioned in (2) above, the wire must be forcibly held by the pressing roller to obtain a strong pressing force or contracting force. Therefore, the wire is subject to be worn out or it deteriorates with the forcibly held point as a center which is the secondary damage. When the wire is made of a hard synthetic resin as is generally used, in particular, the damage spreads in an accelerating manner and durability is not maintained sufficiently. Furthermore, the force for holding the wire creates a large load for the motor that drives the drum; i.e., a motor which produces a large amount of power is required, and the mechanism is subjected to be worn out to a considerable degree. Since a large holding force must be applied as described above, the rotary member and the pressing roller must inevitably be made of a strong material such as a metal which requires countermeasure against rust.
In the device of the pinion-rack type mentioned in (3) above, teeth that are molded on the wire produces distortion which cause variance in the durability; i.e., stable durability is not obtained. With the teeth being formed as described above, furthermore, the strength of the wire becomes inferior to that of the straight wire of the same diameter (without teeth), whereby buckling phenomenon takes place to a considerably degree. Under low-temperature and freezing conditions such as in cold regions, in particular, the frequency of trouble increases inevitably. Moreover, the wire is produced through an increased number of steps that result in an increase in the manufacturing cost.
In the device of the tenor type described in (4) above, the scars of nail are given to the wire by the nails of the rotary member. Further, the scars of nail are given to different positions of the wire due to the rotary motion or a change is temperature. That is, the scars are formed irregularly, and the wire is damaged and is easily broken. In order to prevent a round wire from escaping from the groove of the rotary member, furthermore, it is not allowed to maintain a large gap between the groove of the rotary member and the case body. Therefore, water droplets collect in the gap and freeze. To properly operate the wire, furthermore, the pawls of the rotary member must be composed of a stainless steel or any other metal material.